James A. Hamilton, Ph.D.
Professor, Biomedical Engineering
Professor, Physiology and Biophysics
Research Professor of Medicine
Ph.D., Indiana University
B.S., Juniata College
Phone: (617) 638-5048; Fax: (617) 638-4041
Office: 700 Albany Street, W302
Membrane and Structural Biology; Imaging of fat depots and atherosclerotic plaque.
Research in the Hamilton Group is aimed at providing fundamental information relating to heart disease, diabetes, obesity, and diseases related to fatty acid metabolism. An overall goal to is to develop novel approaches to biomedical issues by integrating physical-chemical and physiological/biochemical approaches. In their newer research this is achieved by assembling multi-disciplinary teams to translate basic research into clinical applications. They use physical and instrumental methods (including solution state 13C NMR spectroscopy, solid state and magic angle spinning multinuclear NMR, multidimensional NMR, MR imaging, and fluorescence) that are tailored to the specific questions we are addressing. These techniques are complemented with molecular modeling, molecular biology and other cell biology methods. Two major areas of their research are described below:
- TRANSPORT OF FATTY ACIDS
The overall aim of research relating to obesity and diabetes is to describe structural and dynamic aspects of fatty acid binding and transport in plasma, in cell membranes, and in the cytosol with state-of-the-art methods in both structural and cell biology. They study fatty acid binding and transport in the plasma by albumin, their transport across the plasma membrane and their binding to intracellular fatty acid binding proteins (FABP). Recently they extended our studies of binding of fatty acids by NMR to an integrated study with NMR, x-ray crystallography, and molecular biology. It is now possible to determine the effect of drugs on fatty acid binding in a site-specific manner, and to locate binding sites of other natural ligands and new drugs by NMR spectroscopy. Their NMR solution structure reveals the same general structural motif as found by x-ray crystallography for several FABP: 10 β-strands running antiparallel to each other, plus two small a-helices, which form a β-barrel. The steroid moiety penetrates deep into the internal binding cavity and the polar glycine is at the aqueous interface. They have published the complete structure of another FABP, the human intestinal FABP and have also determined the structure of a mutation associated with diabetes. Transport of fatty acids through membranes is a highly active area of current research in cell biology. One example of these applications of fluorescence is the monitoring of the transmembrane diffuse (flip-flop) of fatty acids. They developed a hypothesis of fatty acid transmembrane transport that predicts a pH change inside vesicles (or cells) after addition of external fatty acids. Their results show fatty acids flip-flop rapidly across a phospholipid bilayer without a protein transporter. The same approach can be applied to live cells to elucidate pathways of entry of fatty acids into cells. Fatty acid-induced pH changes in cells are being examined by whole cell fluorescence and video imaging fluorescence in single cells under conditions modeling diabetes and obesity.
- ATHEROSCLEROSIS: MAGNETIC RESONANCE IMAGING (MRI) AND NMR SPECTROSCOPY
Another major effort is to develop and apply new NMR and MRI methods for the characterization of lipids in intact atherosclerotic plaques and to correlate NMR spectroscopic data with NMR imaging data. The goals include characterizing lipid phases in specific types of plaques, correlating lipid phase and structures to plaque vulnerability to rupture, and providing information for rigorous interpretation of MR images of plaques. We are studying human, rabbit and mouse plaques. In the rabbit studies they have the opportunity to perform trigger the rupture of a plaque and the formation of a thrombus. In vivo MR imaging has monitored this procedure and MR images detect the newly formed thrombus. This work could translate into the detection of thrombosis in humans and distinction of the thrombus from plaque in a non-invasive way; i.e., MR imaging. Several new publications from their group have reported their continuing development of this application of MRI. After an atherosclerotic vessel (or the plaque itself, as in carotid endarterectomy) is removed from the body, it can be imaged ex vivo at very high resolution. With ex vivo imaging, various pulse sequences can be utilized to highlight different aspects of the atherosclerosis, without the time constraints of vivo imaging. The magic angle spinning (MAS) NMR data from the same segments, together with histology, will aid in interpretation of the fine details of the images.
They are also applying MRI to both mice and men. The remarkable resolution of high-field (11.7T) imaging in a narrow bore that can accommodate mice is shown in the image of the mouse vasculature in a live mouse. At the other end of the spectrum, so to speak, they are imaging obese humans at 3T in a wide-bore clinical study of diabetes. One of our current studies is examining the possible changes in such fat after a diet and exercise program.